1. Field
The disclosure relates to a method, system, and article of manufacture for performing diagnostic operations within a switched fibre channel arbitrated loop system.
2. Background
Fibre Channel is gigabit-speed network technology that may be used for storage networking. In an enterprise or midrange class storage subsystem, the storage devices, such as disk drives, may be arranged as part of a fibre channel arbitrated loop (FCAL) system. This FCAL system allows communication to a set of drives [also referred to as Just a Bunch Of Disks (JBOD)] using the Fibre Channel (FC) interface protocol without having to create a FC fabric, which is expensive and complex to create. In a JBOD configuration the disks are daisy chained together such that all data travels through all drives. As a result when a drive has a problem, it can cause repeated loop configurations and subsequently a loss of access to the entire loop of disks, disrupting the normal flow of Input/Output (I/O) traffic to the disk system.
With the advent and usage of the FCAL switch, thus creating a set of switched drives [also referred to as Switched Branch Of Disks (SBOD)], the above problem can be alleviated to some extent. In a SBOD configuration the disks are connected in a star topology allowing better isolation of problems with disks. Certain FCAL switches can be configured to run a limited diagnostic test before allowing a target drive to be inserted on to the main FCAL loop. This diagnostic, though effective, is primarily a FCAL primitive diagnostic, only testing level-0 FCAL interface operations, such as, testing for signal, synchronization, and successful communications of low level FC ordered sets. Drives can fail across the complete range of FC interface operation level-0 through level 4.